The field of this invention of that of umbilical reels which store and handle hose and/or electric and/or fiber optic control lines for deepwater offshore service. These reels typically pay out these lines, called an umbilicals, and mechanics clamp the umbilical to a drilling riser or other pipe string being run to the seafloor. The actual weight of the umbilical is typically supported in the water by the riser or pipe which the umbilical is attached to. Typically these units only reel up the low load of the umbilical, down to the first clamp, and do not have to winch up the whole weight of the cable.
When the drilling riser or other pipe sting is lowered, an operator will rotate the spool to allow umbilical to be paid off in accordance with the downward movement of the riser or pipe. In some cases, the motor can be left in the take up mode, and the umbilical simply be pulled off the spool against the constant tension provided by the motor power.
The spool portion of a reel can typically be locked into position by brakes, the motor, or a manual locking pin.
A danger to the umbilical or reel can occur in the event that the drilling riser or other pipe string that the umbilical is attached to is lowered when the reel spool is locked a in position. The reel spool can be locked in position because someone forgot to release the locking pin, the brakes are set, or the motor is blocked. When this happens, an umbilical worth hundreds of thousands of dollars can be destroyed, or personnel can be hurt.
Alternately, if the riser is running down and the air pressure which runs the reel is lost on the typical reel, the failsafe brakes will automatically lock and there is again a chance of tearing the umbilical in half before the condition is recognized.
A slip clutch has been added to the drive shaft on some reels to prevent the motor from being able to put too much load on the umbilical, potentially damaging it. When the slip clutch is added to the motor drive shaft, it is ineffective in controlling the maximum loading from the brakes which are unaffected by the motor drive shaft slip clutch.
It would be desirable to have a method of allowing the reel spool to slip when the brakes are set or when the motor is locked in position. Typically, it is not desirable to allow the reel spool to slip when the manual locking pin is in place as that the manual locking pin can be used when personnel might be servicing the reel.